linux-kernel - Re: [PATCHv3 3/3] x86/mm/encrypt: Rewrite sme_pgtable

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Date:   Tue, 30 Jan 2018 16:51:34 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Borislav Petkov <bp@...e.de>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 3/3] x86/mm/encrypt: Rewrite sme_pgtable_calc()

On 1/24/2018 10:36 AM, Kirill A. Shutemov wrote:
> sme_pgtable_calc() is unnecessary complex. It can be re-written in a
> more stream-lined way.
> 
> As a side effect, we would get the code ready to boot-time switching
> between paging modes.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

Reviewed-by: Tom Lendacky <thomas.lendacky@....com>

> ---
>  arch/x86/mm/mem_encrypt_identity.c | 42 +++++++++++---------------------------
>  1 file changed, 12 insertions(+), 30 deletions(-)
> 
> diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
> index 69635a02ce9e..613686cc56ae 100644
> --- a/arch/x86/mm/mem_encrypt_identity.c
> +++ b/arch/x86/mm/mem_encrypt_identity.c
> @@ -230,8 +230,7 @@ static void __init sme_map_range_decrypted_wp(struct sme_populate_pgd_data *ppd)
>  
>  static unsigned long __init sme_pgtable_calc(unsigned long len)
>  {
> -	unsigned long p4d_size, pud_size, pmd_size, pte_size;
> -	unsigned long total;
> +	unsigned long entries = 0, tables = 0;
>  
>  	/*
>  	 * Perform a relatively simplistic calculation of the pagetable
> @@ -245,42 +244,25 @@ static unsigned long __init sme_pgtable_calc(unsigned long len)
>  	 * Incrementing the count for each covers the case where the addresses
>  	 * cross entries.
>  	 */
> -	if (IS_ENABLED(CONFIG_X86_5LEVEL)) {
> -		p4d_size = (ALIGN(len, PGDIR_SIZE) / PGDIR_SIZE) + 1;
> -		p4d_size *= sizeof(p4d_t) * PTRS_PER_P4D;
> -		pud_size = (ALIGN(len, P4D_SIZE) / P4D_SIZE) + 1;
> -		pud_size *= sizeof(pud_t) * PTRS_PER_PUD;
> -	} else {
> -		p4d_size = 0;
> -		pud_size = (ALIGN(len, PGDIR_SIZE) / PGDIR_SIZE) + 1;
> -		pud_size *= sizeof(pud_t) * PTRS_PER_PUD;
> -	}
> -	pmd_size = (ALIGN(len, PUD_SIZE) / PUD_SIZE) + 1;
> -	pmd_size *= sizeof(pmd_t) * PTRS_PER_PMD;
> -	pte_size = 2 * sizeof(pte_t) * PTRS_PER_PTE;
>  
> -	total = p4d_size + pud_size + pmd_size + pte_size;
> +	/* PGDIR_SIZE is equal to P4D_SIZE on 4-level machine. */
> +	if (PTRS_PER_P4D > 1)
> +		entries += (DIV_ROUND_UP(len, PGDIR_SIZE) + 1) * sizeof(p4d_t) * PTRS_PER_P4D;
> +	entries += (DIV_ROUND_UP(len, P4D_SIZE) + 1) * sizeof(pud_t) * PTRS_PER_PUD;
> +	entries += (DIV_ROUND_UP(len, PUD_SIZE) + 1) * sizeof(pmd_t) * PTRS_PER_PMD;
> +	entries += 2 * sizeof(pte_t) * PTRS_PER_PTE;
>  
>  	/*
>  	 * Now calculate the added pagetable structures needed to populate
>  	 * the new pagetables.
>  	 */
> -	if (IS_ENABLED(CONFIG_X86_5LEVEL)) {
> -		p4d_size = ALIGN(total, PGDIR_SIZE) / PGDIR_SIZE;
> -		p4d_size *= sizeof(p4d_t) * PTRS_PER_P4D;
> -		pud_size = ALIGN(total, P4D_SIZE) / P4D_SIZE;
> -		pud_size *= sizeof(pud_t) * PTRS_PER_PUD;
> -	} else {
> -		p4d_size = 0;
> -		pud_size = ALIGN(total, PGDIR_SIZE) / PGDIR_SIZE;
> -		pud_size *= sizeof(pud_t) * PTRS_PER_PUD;
> -	}
> -	pmd_size = ALIGN(total, PUD_SIZE) / PUD_SIZE;
> -	pmd_size *= sizeof(pmd_t) * PTRS_PER_PMD;
>  
> -	total += p4d_size + pud_size + pmd_size;
> +	if (PTRS_PER_P4D > 1)
> +		tables += DIV_ROUND_UP(entries, PGDIR_SIZE) * sizeof(p4d_t) * PTRS_PER_P4D;
> +	tables += DIV_ROUND_UP(entries, P4D_SIZE) * sizeof(pud_t) * PTRS_PER_PUD;
> +	tables += DIV_ROUND_UP(entries, PUD_SIZE) * sizeof(pmd_t) * PTRS_PER_PMD;
>  
> -	return total;
> +	return entries + tables;
>  }
>  
>  void __init __nostackprotector sme_encrypt_kernel(struct boot_params *bp)
>